In recent years, in some cases, operations of various safety devices such as a seat belt and an air bag have been controlled in accordance with a weight of a passenger seated on a vehicle seat for the purpose of enhancing performance of the safety devices. In a conventional passenger's weight measurement device that measures the weight of the seated passenger, a load sensor is interposed between a vehicle floor and the vehicle seat (for example, refer to Patent Document 1 and Patent Document 2).    Patent Document 1: JP A H8-164039    Patent Document 2: JP A H9-207638